Metering devices, such as utility meters, are sometimes tampered with by dishonest individuals who wish to avoid paying for the full amount of utilities they use, for example. Furthermore, point-of-sale devices, such as cash registers or vending machines, may also be subject to tampering by thieves, vandals, etc.
Various prior art approaches have been used for detecting and reporting tampering with such devices. By way of example, U.S. Pat. No. 6,236,197 to Holdsclaw et al. is directed to an apparatus for detecting tampering in a multi-phase electric meter. More particularly, this is done by determining the loss of a reference voltage (indicating possible tampering) in a two-element electronic meter. To determine if the reference voltage of the meter in a 3-wire delta or network installation has been lost, a measurement of the phase angle difference between the two phases is made. If the phase difference is equal to a predetermined value, the meter indicates on a display that a loss of reference voltage and possible tampering has taken place. The apparatus may also be adapted to determine a length of time from when the condition occurred so that the appropriate enforcement and/or billing agencies may be informed. In particular, when an abnormal condition is detected by the meter, warnings may be time and date stamped and logged in an event log, and the number of events and cumulative time of the conditions may be separately logged in an occurrence log. The logs are stored in an EEPROM which may be accessed through software for further diagnostic processing and evaluation external to the meter.
Another approach is provided in U.S. Pat. No. 6,357,007 to Cromer et al. This patent discloses a system for monitoring tamper events in a computer system connected to a network. The system includes a tamper real time clock (RTC) which receives a tamper event signal from the computer system. The tamper RTC includes a timer for indicating the time of a tamper event, and a management device for receiving the tamper event signal. The management device issues a command to the tamper RTC to obtain the time of the tamper event. The management device also generates a network packet which includes the time of the tamper event to a system administrator of the network.
Despite the advantages of the above tamper detection approaches, further tamper indication functionality may be required in some applications.